(1) Field of the Invention
The present invention relates to a method of fabricating the capacitors of dynamic random access memory (DRAM) cells, and more particularly to the single-side corrugated cylindrical capacitor structure of high density DRAMs.
(2) Description of the Related Art
A DRAM cell comprises a metal-oxide-semiconductor field effect transistor (MOSFET) and capacitors which are built in a semiconductor silicon substrate. There is an electrical contact between the source of a MOSFET and the storage node of the adjacent capacitor, forming a memory cell of the DRAM device. A large number of memory cells make up the cell arrays which combine with the peripheral circuit to produce DRAMs.
In recent years, the sizes of the MOSFETs and capacitors have become continuously smaller so that the packing densities of these DRAM devices have increased considerable. For example, a number of semiconductor manufacturing companies in the world have already begun mass production of 16M bit or even 64M bit DRAMs.
In order to achieve high packing density, the cell size of a DRAM cell must shrink. As the sizes of the capacitors become smaller, so as the capacitance values of the capacitors are decreasing, that reduces the signal to noise ratio of the DRAM circuits, causing the performance problem. In order to maintain or even increase the value of the capacitance for smaller size capacitors, increasing the surface area of the polysilicon storage nodes or reducing the thickness of the dielectric layer is necessary.
Various shapes of capacitor structures have been used to address this issue. U.S. Pat. No. 5,185,282 to Lee et al. (the entire disclosure of which is herein incorporated by reference) provides a method of fabricating cup-shaped capacitor storage node. Another U.S. Pat. No. 5,021,357 to Taguchi et al. (the entire disclosure of which is herein incorporated by reference) supplies a method of fabricating fin structure capacitor electrode. These capacitor structures can effectively increase the capacitance values of the capacitors, however these processes are too complicated and highly fastidious. So they are difficult to be practically employed for mass-production.
Most recently, H. Watanabe et al. in IEDM 92 (the entire disclosure of which is herein incorporated by reference) discloses a method of fabricating cylindrical capacitor electrode. Please refer to FIG. 1, the cylindrical capacitor structure 5 increases the capacitor surface area tremendously without increasing the silicon area. The cylindrical capacitor structure is also more stable than the fin capacitor structure.
The present invention discloses a new method to fabricate high-capacitance cylindrical capacitors of high density DRAMs which further increases the capacitor surface area.